The present invention pertains generally to radar systems and methods. More particularly, the present invention pertains to radar systems and methods for wide area surveillance including targeting/tracking of multiple, stationary and moving objects. The present invention is particularly, but not exclusively, useful for wide area surveillance with a plurality of close-range radars.
Wide area radar surveillance has both military and commercial applications. Military applications of wide area radar surveillance typically include detecting and tracking hostile forces including fast moving vehicles, and guiding weapons to target. Typical commercial applications of wide area radar surveillance can include traffic flow monitoring, and search and rescue.
For all the above-described applications, it would be desirable to have a high-resolution radar system that can detect and track multiple objects including stationary and fast moving objects. Further, a desirable system would be effective in all types of terrain and weather conditions. For a relatively small surveillance area (e.g. 400 km2), these objectives have heretofore been achieved using a single, close range radar. For example, a manned or unmanned surveillance aircraft equipped with a close range radar can be stationed in tight orbit over the small surveillance area and used to detect and track stationary and fast moving objects. Although this arrangement has provided reasonable resolution in all types of terrain and in adverse weather, the size of the surveillance area has been limited.
An additional drawback associated with the use of a single, close range radar concerns the tracking of fast moving objects. Specifically, if a tracked object leaves the small surveillance area, the surveillance aircraft must follow the object or discontinue tracking. If the surveillance aircraft follows the moving object, the surveillance aircraft may have to discontinue surveillance of other objects in the original surveillance area. Furthermore, following the object requires a fast moving, agile radar platform, increasing system cost and complexity.
In addition to the above-described deficiencies, the use of a single close range radar to scan a surveillance area provides only reasonable resolution. On the other hand, when two or more radars are used to scan a surveillance area, the resultant radar datastreams can be multilaterated using signal processing techniques to reduce azimuthal geolocation error and increase resolution. However, effective multilateration requires the angle between the horizontal components of the radar beams (i.e. the multilateration angle) to deviate from zero degrees (0xc2x0) and one hundred eighty degrees (180xc2x0). One way to ensure that a proper multilateration angle is maintained is to synchronize the movements of the radar platforms. Of course, platform synchronization increases system complexity and cost.
In light of the above, it is an object of the present invention to provide radar systems and methods for wide area surveillance and targeting/tracking of stationary and moving objects within the surveillance area. It is another object of the present invention to provide radar systems and methods for wide area surveillance that are effective in all types of terrain and in adverse weather. It is yet another object of the present invention to provide radar systems and methods for wide area surveillance having resolutions that are substantially equivalent to the resolutions obtainable with multilaterated, close range radar systems. Yet another object of the present invention is to provide radar systems and methods for wide area surveillance that are capable of tracking an object moving through the surveillance area without following the object with a radar platform. Still another object of the present invention is to provide radar systems and methods for wide area surveillance which achieve good multilateration without synchronizing the movements of the radar platforms. It is still another object of the present invention is to provide radar systems and methods for wide area surveillance that have minimal system complexity, are relatively simple to implement, and comparatively cost effective.
The present invention is directed to a system and method for detecting and tracking an object in a surveillance area. For the present invention, the surveillance area is partitioned into a plurality of cells. Each cell is scanned contemporaneously by at least two radars to produce two (or more) respective datastreams for the cell. The resulting datastreams for each cell are then combined by a processor to produce a multilaterated datastream for each cell. The multilaterated datastreams for all cells are subsequently combined and the resulting data used to detect and track one or more objects in the surveillance area.
In a particular embodiment of the present invention, the surveillance area is divided into hexagonally shaped cells. In this embodiment, a plurality of unmanned air vehicles (UAV), each equipped with Ground Moving Target Indicator (GMTI) radar, are provided one UAV for each hexagonally shaped cell. In greater detail, each GMTI radar equipped UAV is instructed to tightly orbit over the center of one hexagonally shaped cell. While orbiting the center of the cell, each GMTI radar equipped UAV scans two adjacent cells. As explained further below, this cooperation of structure allows each cell to be scanned contemporaneously by two different radars. Additionally, this cell geometry and radar positioning scheme provides good multilateration because the horizontal components of the radar beams within a cell cannot be co-linear. Also, as detailed further below, this geometry allows the orbit of one GMTI radar equipped UAV to be asynchronous relative to the orbit of the other GMTI radar equipped UAV""s without degrading the multilateration angle.
In this particular embodiment, synthetic aperture radar (SAR) can be used in addition to the GMTI radar to produce a stationary image of the surveillance area and to periodically check for stopped vehicles. In one implementation, two SAR radars are used for a six cell surveillance area, with the SAR radars mounted on UAV""s that orbit at a higher elevation above the surveillance area than the GMTI radar equipped UAV""s. As intended for the resent invention, the GMTI radar can be operated in a coarse resolution ode for use in multilateration of the entire cell or a high-range resolution mode (HRR) for aid in classifying, identifying and/or tracking a detected object. In a low system bandwidth implementation of the present invention, the HRR mode GMTI and the SAR time-share a common frequency band while a separate frequency is assigned to each radar for coarse resolution mode GMTI.
Datastreams from each radar are sent via high-speed datalink to a Data Control Manager (DCM), which performs multilateration for all cells. The DCM then mosaics and fuses the multilaterated datastreams, allowing objects to be tracked as they move from cell to cell. Specifically, the DCM can extrapolate an object""s position based on the object""s kinematics to determine when an object has crossed a cell boundary and entered a new cell. The DCM then detects the object in the new cell""s multilaterated datastream. This process can be confirmed using HRR mode radar. The high-speed datalink between the DCM and radars can also be used to direct the radars for targeting, to monitor and control the UAV orbits, and to direct weapons. Ground control stations (GCS) are provided for routine control and status of the UAV""s and radars via a moderate speed datalink. A network connects each GCS in communication with the DCM.